A double-flywheel damper of this type is known already, in particular from the document FR-A-2714131, which describes a double-flywheel damper in which the torsion damper includes an epicyclic gear train. In one embodiment described in the above prior art document, the sun gear is driven in rotation by a first inertia mass fastened to the crankshaft of an internal combustion engine, the outer crown wheel is fastened to the second inertia mass, and coil springs are mounted in a chamber delimited by the first inertia mass between that first inertia mass and the planet gear carrier, between the first inertia mass and the outer crown wheel or between the outer crown wheel and the planet gear carrier.
One advantage of using an epicyclic gear train in the torsion damper of a double-flywheel damper is the transmission of torque between the two inertia masses with a transmission ratio determined by the epicyclic gear train. However, the embodiments described in the document FR-A-2714131 have the drawback that the springs of the torsion damper, which are driven in rotation with the inertia masses and are situated at the external periphery of those inertia masses, are very sensitive to centrifugal forces and have a hysteresis that increases when the rotation speed increases, with risks of blocking and jerky operation.